The present invention relates to a device for reflecting light also called an optical reflection plug.
When building optical systems for various applications and special devices, there may be a need for providing a total reflection of light. At present there is no good established method to produce a total reflection of light independently of the wavelength of the light. Metallizing the end of the waveguide by aluminum has been mentioned as a possible way, see M. V. Bazylenko, M. Gross, E. Gauja, and P. L. Cchu, xe2x80x9cFabrication of Light-Turning Mirrors in Buried-Channel Silica Waveguides for Monolithic and Hybrid Integrationxe2x80x9d, J. Lightwave Technol. Vol. 15(1), pp. 148-153, 1997. When making optical integrated circuits having integrated waveguides metallization of vertical end surfaces is a costly and complicated process. Also the lifetime can be questioned. A method of producing total reflection for a relatively narrow wavelength range is to use Bragg gratings. Using special designs such as varying the grating period in the propagation direction a total reflection over a wider range could possibly be achieved. However, it is relatively costly to produce Bragg gratings and the production thereof requires costly equipment as well as a large area on the chip in the case where the totally reflecting structure is to be incorporated in an integrated circuit structure.
In L. V. Iogansen et al., xe2x80x9cMultimode fiber interferometersxe2x80x9d, Optics and Spectroscopy, Vol. 58, No. 5, May 1985 optical reflectors using resonant tunnel loop reflection are disclosed. Simple loop reflectors are shown in FIG. 5 in this document. There are some losses in such a loop reflector comprising loss in the waveguide, loss in the tunnel-coupling section, and loss of radiation in the loop.
In the Japanese patent application JP 8-274398 a semiconductor laser module is disclosed. It has a loop mirror comprising a four-terminal fiber coupler and a fiber loop connected to the coupler.
It is an object of the invention to provide a device for reflecting light waves to be easily incorporated in integrated optical circuits.
A device for reflecting light waves is built on a substrate and has a planar structure. It comprises a light power coupler operating as a power splitter, preferably of the MMI-type, and configured as a rectangular plate at or in the surface of the substrate. The coupler splits light incoming on an input terminal into at least two equal portions, each portion delivered on an output terminal. Also the coupler combines light incoming on at least two output terminals into combined light delivered on the input terminal. A loop is connected to two output terminals for conducting light delivered on each one of these output terminals back into the other one of these output terminals. The loop is a planar waveguide built on the substrate, connected to an edge surface of the coupler. The loop has preferably an outer contour comprising a multitude of linear segments and it can also have an inner contour comprising a multitude of linear segments. The shape of the loop can e.g. be formed by folding a strip having a uniform width at least twice, the folds being symmetrically made.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.